There are two modes operation of Emergency lighting module,
a) Charging mode operation (SMPS): -
In Emergency lighting module low power SMPS is used for battery charging operation. The input filter circuit attenuates the high frequency noise generated by the switching circuit. The AC voltage is rectified and then filtered. The switching and control IC TNY277 is used. IC consists of an oscillator, enable circuit (sense and logic), current limit state machine, 5.85 V regulator, bypass/multi-function pin under voltage, over voltage circuit, and Current limit selection circuitry, over- temperature protection, current limit circuit, leading edge blanking, and a 700 V power MOSFET. Tiny Switch-III incorporates additional circuitry for Line under voltage sense, auto-restart, adaptive switching cycle on-time extension, and frequency jitter. This MOSFET switches high frequency i.e. ON/OFF, control to regulate the output voltage. Feedback pin EN/UV enables input and line under voltage. Isolated step-down transformer used, converts the high frequency switching voltage to low output voltage. This voltage is rectified using high frequency rectifier diode and filter.
The generated output DC voltage is used for battery charging in constant current mode.
b) Inverter (Discharging mode) operation: -
A Push-Pull circuit two MOSFET based fly back mode inverter is built to drive a lamp in emergency mode. A controller based AT tiny 45 which generates PWM is high frequency square wave (22-35 KHz) as a gate drive for a MOSFET. Generated PWM before drive to MOSFET it amplifies by using totem pole circuit then drive the MOSFET. The isolated step up transformer used, generates the high voltage required to keep the lamp ON; with battery in fully charged condition, backup time of 2 hours can be achieved. Protections like No load protection
While most of the applications used simple battery charger and inverter function, there are some premium models available in the market with self test feature and integration of emergency lighting with DALI (Digital Addressable Lighting Interface) based lighting system. However explained product is intended for middle market segment with cost effective solution.